MisV1306: New Eccentric Binary

2005 Oct. 13
Seiichi Yoshida / MISAO Project

We discovered an unusual eclipsing variable MisV1306, a new eccentric
binary. We have been discovering many new eclipsing variables in the
course of the MISAO Project, but this is our first discovery of an
eccentric binary.

The types and periods of our new eclipsing variables are revealed by
Kazuhiro Nakajima, Mie, Japan, based on his thorough observations.

Recently, it became easy to reveal the types and periods of eclipsing
variables using the huge amount of observations of automated surveys.
But it is not easy still now on some stars. Nakajima observed MisV1306
on 70 nights during about 2 years, measured 1812 observations, and
finally succeeded to clarify the type and period of this star. The
result is very interesting.

Discovery of a variable star MisV1306

MisV1306 is a new variable star discovered among the unfiltered CCD
images taken by Nobuo Ohkura, Okayama, Japan. It was picked up by
Seiichi Yoshida, MISAO Project, from the candidates of new variable
stars detected automatically by the PIXY system 2. The variation was
confirmed by Ken-ichi Kadota, MISAO Project.

MisV1306 locates at R.A. 02h03m28s.28, Decl. +58o54'13".8 (2000.0),
around the border between Cassiopeia and Perseus, near by Double
Clusters. The brightness is 12 mag, visible visually using a
telescope.

Created by Kazuhiro Nakajima

It was visible on 9 night images between 1999 Sept. 27 and 2001
Nov. 21 taken by Ohkura and Kadota. The brightness has been constant
except for one night, 2001 Nov. 20, when it faded by about 0.6 mag.

This light curve suggests that it is an Algol-type eclipsing variable,
almost constant usually but sometimes fades out in a short time. So we
announced it as the 1306-th new variable star of the MISAO Project,
MisV1306, on 2005 July 3.

Quest of the eccentricity

We asked Nakajima for time series photometry of this star as one of
the candidates of eclipsing variables in 2003 when we noticed the
variation for the first time. Nakajima started the observation on 2004
Jan. 21.

Fortunately, Nakajima succeeded to catch the first eclipse on the
third night. But unexpectedly, it became a very hard work to reveal
the character of this star after that. It took about 2 years until he
found the unusual eccentric variation and determined the accurate
period.

Nakajima described the hard process to reveal the character of the
eccentric binary MisV1306 as follows.

I could catch the eclipse on the third night, so it seemed to easy
to conclude soon. I could catch the second eclipse on the 22th
night. However, the work became difficult after that.

I calculated 5 predictions of possible periods based on the two
eclipses and tried to catch the next eclipse. But I failed.

An eclipsing variable continues periodic fading repeatedly. When two
eclipses are caught, the possible period can be presumed assuming the
number of missing eclipses between them. Then next fading can be
predicted. If the star fades out as predicted, it means the presumed
period is correct.

However, in the case of an eccentric binary, the intervals between
eclipses do not become constant. So, the next fading does not occur as
predicted, and it becomes difficult to clarify the correct period.

Therefore, I gave up my predictions and started daily observations
to catch unexpected eclipses as before. I could catch an eclipse
on the 49th night. But it was impossible to see the periodic
character from the three eclipses. So I continued observations
every day.

I could catch the secondary minimum on the 55th night. Then I
finally noticed the eccentricity. I calculated the eccentric
period, and succeeded to find the rough period of 5.337 days.

After that, I could observe it based on my prediction. However,
the condition in this year was not good. The period of 5.337 days
means I can observe the minimum every 16 days and 13 minutes, but
some primary minima coincided to the full moon.

Finally, MisV1306 was revealed to be an eccentric binary with a period
of 5.3364 days, and unfiltered CCD variations of 11.97 mag at maximum,
12.50 mag at primary minimum, 12.30 mag at secondary minimum. The
secondary minimum occurs at the phase of 0.412. It took 70 nights
until 2005 Sept. 18 to get this result.

Created by Kazuhiro Nakajima

It took 70 nights, about one and a half year. I did not imagine
the eccentricity at first. I calculated many possible periods and
tried to observe. I was relieved when I caught the secondary
minimum.

This is the most difficult and confusing target among the new
eclipsing variable stars of the MISAO Project.

Further story of MisV1306

Recently, we can see the huge amount of observations of automated
surveys for bright variable stars. The Northern Sky Variability Survey
(NSVS) in the Northern Hemisphere, and the All Sky Automated Survey
(ASAS) in the Southern Hemisphere are available.

MisV1306, locating in the Northern Hemisphere, is recorded by the
NSVS. We can see the light curve by the NSVS at: